Last year a remarkable exhibit came to light. Hidden
in the vaults of a London museum was a scrap of paper containing a few
strands of hair.

The paper was crudely fashioned into an envelope but
the words on it immediately caused a stir: "Hair of His Late Majesty,
King George 3rd."

For Professor Martin Warren, it was the clue that would
help him finally solve the mystery of King George's illness. His investigation
is featured in a BBC documentary, Medical Mysteries.

"King George is largely remembered for those periods
when he lost his mind. But it's been difficult to explain these attacks,
so I was keen to analyse this hair sample," said Professor Warren.

When the hair was tested by the Harwell International
Business Centre for Science & Technology in Didcot, Oxfordshire, the
results were surprising.

The king's hair was laden with arsenic. It contained
over 300 times the toxic level.

"This level is way above anything we were expecting
- it's taken us completely by surprise."

More detective work

Far from being an answer, this remarkable finding was
just the start of Warren's detective work.

In King George's time, his bizarre behaviour and wild
outbursts were treated as insanity.

He was bound in a straitjacket and chained to a chair
to control his ravings. King George was officially mad.

It wasn't until the 1970s that a new and controversial
diagnosis was made.

Two psychiatrists - Ida MacAlpine and her son Richard
Hunter - revisited the king's medical records and noticed a key symptom;
dark red urine - a classic and unmistakable sign of a rare blood disorder
called porphyria.

Porphyria can be a devastating disease. In the acute
form, it can cause severe abdominal pain, cramps, and even seizure-like
epileptic fits.

Misdiagnosed

It is frequently misdiagnosed, and even in modern times,
some sufferers have been thought to be mentally ill.

Pauline Bradshaw was 40 when she was finally diagnosed
with acute porphyria.

"I was very confused and frightened, because I didn't
know why I was feeling so bad," she said.

"Every day was this battle, you know, feeling sick
and dizzy not knowing what was wrong or what was causing it."

For years her GP put her symptoms down to depression
and prescribed anti-depressants, but when a relative wrote to say she had
been diagnosed with acute porphyria, Pauline's symptoms fell into place.

Since then, with support from the British Porphyria Association,
she has learnt how to live with this incurable condition.

One of the great mysteries of King George's porphyria
was the severity of his attacks.

It is rare for men to suffer this acute form at all -
normally males show no symptoms.

And - a final puzzle - King George didn't have any attacks
before his 50s.

Arsenic to blame?

Professor Warren knew that porphyria attacks can be triggered
by a wide range of substances - alcohol, common medication, even monthly
hormones. Perhaps arsenic could also be a trigger.

He contacted Professor Tim Cox, an expert on extreme
cases of porphyria at Addenbrookes Hospital in Cambridge.

Professor Cox confirmed his guess - arsenic was listed
as a trigger. And the massive levels found in King George's hair suggested
that the arsenic had been liberally ingested over a long period of time.

The two professors began poring over the King's medical
records preserved in the Royal archive at Windsor.

There was passing reference to arsenic used as a skin
cream, and as wig powder, but nothing that could explain the staggering
levels of arsenic showing up in the king's hair.

The most common medication he was given was James' powders,
a routine medicine he was being given several times a day - made of a substance
called antimony.

Final clue

Tracking down James' powders at the Royal Pharmaceutical
Society, Warren found the final piece of the puzzle in a 19th century almanac.

Antimony, even when purified, contains significant traces
of arsenic.

The arsenic from the very medication he was being given
to control his "madness" was triggering more attacks.

His porphyric attacks had been brought on after a lifetime's
arsenic accumulated in his body, and then were made much more prolonged
and more severe by the medicine to treat him.

For professor it is the end of a long trail.

"It is a very convincing explanation of the king's
attacks, and could account for why he had them at such a late stage in
life and why they were so severe.